Deploying green hydrogen to decarbonize China’s coal chemical sector

China’s coal chemical sector uses coal as both a fuel and feedstock and its increasing greenhouse gas (GHG) emissions are hard to abate by electrification alone. Here we explore the GHG mitigation potential and costs for onsite deployment of green H2 and O2 in China’s coal chemical sector, using a life-cycle assessment and techno-economic analyses. We estimate that China’s coal chemical production resulted in GHG emissions of 1.1 gigaton CO2 equivalent (GtCO2eq) in 2020, equal to 9% of national emissions. We project GHG emissions from China’s coal chemical production in 2030 to be 1.3 GtCO2eq, ~50% of which can be reduced by using solar or wind power-based electrolytic H2 and O2 to replace coal-based H2 and air separation-based O2 at a cost of 10 or 153 Chinese Yuan (CNY)/tCO2eq, respectively. We suggest that provincial regions determine whether to use solar or wind power for water electrolysis based on lowest cost options, which collectively reduce 53% of the 2030 baseline GHG emissions at a cost of 9 CNY/tCO2eq. Inner Mongolia, Shaanxi, Ningxia, and Xinjiang collectively account for 52% of total GHG mitigation with net cost reductions. These regions are well suited for pilot policies to advance demonstration projects.


REVIEWER COMMENTS
Reviewer #1 (Remarks to the Author): This paper has done an impressive work on the deploying green hydrogen to cecarbonize China's coal chemical sector through exploring GHG mitigation potential and costs.The GHG mitigation potential and costs for onsite deployment of green hydrogen, green oxygen, and renewable electricity in China's coal chemical sector are examined via deploying onsite solar and wind power combined with water electrolysis.The paper is welly organized and the content is interesting.The authors provided detailed source data in supplementary information to support the data credibility, data processing and the accuracy of analysis and conclusion.I believe this paper has a certain guiding significance for the development of China's coal chemical industry in the 14th Five-Year pefiod.I recommend this paper to be published in Nature Communications after a revision.Major: However, there is a key issue which need the authors to think and practice.This issue is how to realize the coupling and integration of coal chemical sector and renewable energy.The renewable energy, e.g., wind and solar energy, is intermittent and volatile, while the coal chemical sector is continuous and stable.How to achieve optimal matching between the renewable energy and coal chemical sector.This is a system engineering problem.Different matching will lead to large influence of the GHG mitigation potential and costs.As the amount of renewable wind and solar energy in different provinces in China varies greatly, and the development of the coal chemical industry is alao different, i.e., resources, policies, etc.The models of GHG mitigation potential and costs used in this paper are linear models, which cannot really reflect the volatility of both the supply side and the demand side.In fact, I hope the authors can finally give some constructive suggestions and prospects, such as how to integrate coal chemical industry and renewable energy in different provinces or regions (composed of several provinces) in China, and the degree of renewable energy alternative in the medium and longterm development of coal chemical industry.Minior: The methods section in this paper should be put befor the conclusion.It is not clear how the GHG mitigation potential and costs are calculated.Please provide the detailed calculation models of the GHG mitigation potential and costs in the Supplementary Information.I am not sure if CNY is acceptable by the journal.Format the reference in Line 501, Page 21.Provide the website source.
Reviewer #2 (Remarks to the Author): The authors estimate China's coal chemical production resulted in substantial GHG emissions and discuss the effect of whether to use onsite solar or wind power for water electrolysis on GHG emissions and coal chemical product costs.The onsite deployment of renewables-based electrolytic H2 and O2 to replace coal-based H2 and air separation-based O2 in the coal chemical sector in the onsite solar electricity (SE) scenario and onsite wind electricity (WE) scenario can reduce 50% and 52%, respectively, of 2030 baseline GHG emissions from coal chemical production in China.The results are very instructive for the decarbonization pathway for China's coal chemical sector.In my opinion, the manuscript is adapted for publication upon some minor modifications, as detailed in the following.1.In Page 6, the authors find that "MG and HG scenarios increase GHG emissions by 35% and 15% (448 and 183 MtCO2eq), respectively, relative to the baseline scenario"."However, the SE and WE scenarios substantially reduce GHG emissions by 50% and 52% (632 and 659 MtCO2eq), respectively, relative to the baseline scenario".This result may be related to CO2 emissions from grid electricity consists of coal, hydro, wind, solar nuclear, gas and biomass and others.Please provide a supplementary explanation of the CO2 emission factors of various types of electricity.2. There is no production of traditional coal chemicals and modern coal chemicals in Beijing or Tibet.So there seems to be no need for water electrolysis for the coal chemical sector in these two regions.This is also consistent with Supplementary Table S14.However, in Page 8, the authors inference that most provinces "increase their GHG emissions relative to the baseline scenario" and the Figure 3 show the increase of CO2 emission for Bejing and Tibet.The inconsistency of the data is confusing.3.In Page 9, "However, Jiangsu, Zhejiang, and Jiangxi slightly increase their GHG emissions", ….., "This is because the three provinces produce the majority (~60%) of solar panels in China which results in additional GHG emissions".Whether are there duplicate statistics for CO2 emissions of solar panels and the life-cycle GHG emission of solar/wind electricity?In particular, explain the source and composition of the data in Figure 3. 4. The meaning of "Electricity for other operations" in Figure 2 and Table 2 is unclear, how is the data obtained?Please provide a supplementary explanation.5. Solar radiation and wind speed vary from province to province in China.The authors suggest that "provinces determine whether to use onsite solar or wind power for water electrolysis based on their lowest cost options".How do the authors take into account the natural resource condition?6. Electricity price is an important basis to discuss the cost of hydrogen production by water electrolysis.In Page 14, "Since onsite renewable electricity is cheaper than grid electricity, GHG mitigation costs when using renewables-based water electrolysis are much lower than when using grid electricity-based".However, according to Supplementary Table S20, "an operating cost of 33 USD/kW in 2030", the price of electricity is much higher than that of grid electricity.The cost parameters for provincial solar and wind electricity generation are much lower that of grid electricity as shown in Supplementary Table S21.Data consistency in calculating costs needs to be explained.7. Please state what "+" "-" represent in the Table 2.
Reviewer #3 (Remarks to the Author): This paper gives detailed analysis of GHG emission and cost about deploying green hydrogen to decarbonize China's coal chemical sector.Two comments: 1.What is the scientific value of this study?Please give more clear and detailed conclusions.2.In the analysis, hydrogen storage and transportation seems not be considered.Will they affect the carbon emission and cost of green hydrogen to decarbonize coal chemical sector?
Reviewer #5 (Remarks to the Author): The present paper investigates examine the GHG mitigation potential and costs for onsite deployment of green hydrogen, green oxygen, and renewable electricity in China's coal chemical sector, via deploying onsite solar and wind power combined with water electrolysis.The topic presented in this work is really interesting.However, several modifications are required: I analyze the single sections: Abstract has inappropriate structure.I suggest to answer the following aspects: -general contextnovelty of the work -methodology used (describe briefly the main methods or treatments applied)main results and related interpretations.Introduction: This section should briefly place the study in a wide context and emphasize why it is relevant carrying out the analysis.It should define the purpose of the work and its significance.In this perspective, this section is too succinct and fails to effectively point out the relevance of your contribution towards the existing literature.The authors could better introduce the topic by framing it within the energy/sustainability transition dynamics.Some literature is also required to justify the focus on green hydrogen, among the others.Please see: https://doi.org/10.1016/j.cogsc.2021.100506https://doi.org/10.1016/j.respol.2021.104464https://link.springer.com/article/10.1007/s40888-020-00206-4https://doi.org/10.1016/j.eneco.2023.106642Materials and methods: I found this section very important for the readability of the paper.I think the research procedure could be much more clearly described by means of a diagram also highlighting its potential and limit.
Discussions: The discussion of the results is merely descriptive and the obtained evidence is flimsy due to the fact the outcomes are not supported by an adequate discussion in light of scientific literature.Authors should discuss the results and how they can be interpreted in perspective of previous studies and their implications should be discussed in the broadest context possible.
Conclusions: Conclusions must also be revised according to the previous comments.In particular, they should discuss practical and policy implications as well as future lines of research.As it stands now, they fail to extract all the juice of your work.
I hope these comments might help in improving the paper and encourage the authors to move forward.